Polyphenylene ethers are known and described in numerous publications including U.S. Pat. Nos. 3,306,874 and 3,306,875 of Allan S. Hay and U.S. Pat. Nos. 3,257,357 and 3,257,358 of Gelu Stamatoff. The high molecular weight polymers are high performance engineering thermoplastics possessing relatively high melt viscosities and softening points (i.e., in excess of 275.degree. C.) and are useful for many commercial applications requiring high temperature resistance including formation of film, fiber and molded articles.
While their high performance properties are most desirable, the relatively high melt viscosities and softening points of these polyphenylene ethers are often a disadvantage. For example, although they may be employed to produce superior molded articles by melt processing techniques, the high temperatures required are undesirable.
Because of low cost and an overall combination of fair to good properties, alkenyl aromatic resins such as polystyrene have found wide and diversified commercial acceptance. However, such resins are usually brittle, possess relatively low heat distortion temperatures and have relatively poor resistance to the more common organic solvents.
Thermoplastic compositions containing polyphenylene ether (or oxide) in admixture with alkenyl aromatic resins resolve many of the drawbacks of these two individual resins. Examples are, for instance, described in U.S. Pat. No. 3,383,435 of Eric P. Cizek, the disclosure of which is incorporated herein by reference. Such compositions are most generally employed in the production of molded and/or extruded articles.
It is known in the art that various of these properties of these compositions may be further improved by copolymerizing the alkenyl aromatics with other monomers or by blending with other resins. Modifiers such as butadiene, for example, are customarily incorporated into the alkenyl aromatic resins to improve the properties of the resultant compositions. Such modified resins provide means for overcoming various physical drawbacks of alkenyl aromatic resins, particularly polystyrene, while simultaneously facilitating the processing of polyphenylene ethers.
As is described in the art, butadiene modification of alkenyl aromatic resins may take many forms. Polybutadiene or copolymers partially derived from butadiene may be graft, block or otherwise polymerized with such alkenyl aromatic resins. The resultant product may also be unsaturated or saturated (for example, by subsequent hydrogenation) without loss of desirability.
Despite the varied and diverse means for preparing these modified resins, the prior art approaches have generally involved polymerization techniques which developed a continuous alkenyl aromatic phase containing a discrete and discontinuous butadiene phase. These approaches are known to result in improved polyphenylene ether compositions.
An alternative butadiene modified-polyalkenyl aromatic form of resin--i.e., one in which there is a continuous phase including butadiene--is known. Their preparation is described in Polymer Engineering and Science, Vol. 17, page 498. Such resins have not, however, been employed with polyphenylene ethers. No substantial uses have been found for them and they have therefore been largely ignored.
It has now been discovered that this latter class of modified resins may be utilized in producing improved polyphenylene ether compositions. Such compositions, incorporating butadiene-modified alkenyl aromatic derived from a resin having a continuous phase which is butadiene-based, exhibit highly desirable impact strengths and other physical and processing properties.